The invention pertains to the field of intraocular surgery, and, more particularly, to surgical procedures for removal of pre-retinal or post-retinal membranes.
It is a frequent post-operative complication following surgical procedures in the posterior region of the eye that a glia cell membrane will form and attach itself to the retina. Anytime the choroid layer is stimulated such as by cutting, laser burning, lesion caused by probing or cryo or thermal damage, or any other form of stimulation, fibro and glia cells will be pumped from the choroid by pneumatic processes. Glia cells are glue-like and serve to repair damage surrounding the lesion formed by the stimulation. This excretion of glia cells is often used to "glue" a detached retina to the choroid. Unfortunately, the body's control mechanisms of secretion of fibro and glia cells are not finely tuned enough to stop secretion of the cells at the precise time when enough cells have been excreted to do the job. Excretion of excess cells often results in formation of a membrane of cells over the retina between the retina and the lens of the eye resulting in obstruction of the light path to the retina. Sometimes, in the case of detached retinas, the membrane forms between the retina and the choroid.
The formation of these membranes is called proliferative disease. This disease frequently is a post-operative complication of surgical procedures for reattachment of detached retinas. One of the negative effects that results from this phenomenon is that the glia cells initially form a single cell layer membrane over the retina or between the retina and the choroid. This membrane is attached to the retina at various points by what are sometimes referred to as "nails". The retina is normally attached to the choroid by a structure which is similar to VELCRO.TM. brand hook and loop fabric.
There is a problem of spontaneous detachment of the retina if proliferative disease develops. This can occur for the following reason. The membranes initially form as a single cell layer. Later, the cells often rearrange themselves into a multiple cell layer without growing further. Attachments to the retina at the locations of the "nails" may be quite strong. Because the same number of cells that were formerly a single cell layer have become a multiple cell thickness layer, the membrane tends to shrink. This shrinkage causes stresses on the retina at the positions of the "nails" which can result in holes being pulled in the retina or in spontaneous detachment of the retina from the choroid.
Another problem of membrane formation is that in the prior art process for removing such membranes, forces can be applied to the retina by the tools used or through the "nail" connection points to damage the retina structure. Typically, this happens by pulling a hole in the retina at the position of a nail or by punching a hole in the retina through mistakes in manipulation of the tools used. Also, the process of removing a post-retinal membrane, i.e., one between the retina and the choroid, can result in cutting off circulation of blood to the rods and cones of the retina. To understand these problems further, consider the following.
In the prior art, surgeons have removed these membranes from the retina using several techniques. One such technique is to take a vertical intraocular scissors with the blades closed and insert the tip of the scissors between the membrane and the retina. This is a very delicate process and requires great manual dexterity since the space between the membrane and the retina is not large. After the scissors are inserted, the blades are very gently opened to separate the membrane from the retina. This process is continued until the location of a "nail" is encountered. Then a horizontal intraocular scissor is inserted in the space between the cell membrane and the retina in such a manner as to cut the "nail". This process is repeated until the "nails" have been found and severed or pulled loose. After the cell membrane has been separated in this manner from the retina, it is usually removed using a vitrectomy probe.
Another prior art technique is to use an instrument which has a fiber-optic probe with a hook. The hook is very small and is formed of the tip of the light pipe. The hook is used by inserting its tip between the membrane and the retina and separating the membrane from the retina by pulling gently on the membrane.
The difficulty with both of these prior art approaches is that damage to the retina can easily result. One type of damage can result if the mechanical forces applied to the membrane and transmitted to the retina at the locations of the "nail" are too large. This can result in holes being pulled in the retina at the position of the "nails". Further, detachment of the retina from the choroid can also result if the force exerted on the retina through the nails exceeds the force holding the retina to the choroid. Another type of damage that can result is through inadvertent movement of the instrument while the retina is engaged on the hook which results in excessive force being applied to the retina. If the tools are not manipulated with great skill, holes can be poked in the retina. These holes result from the relatively concentrated forces acting on the retina at the tips of the instruments. Even a slight misapplication of force can result in this type of damage to the retina.
Accordingly, a need has arisen for a system which can be used to gently separate the membranes from the retina without causing spontaneous detachment of the retina and without pulling or punching holes in the retina thereby allowing the "nails" to be cut without damage to the retina.